Today there was said to be a mysterious invite only Assassin's Creed event which MCV (a UK magazine) attended. The details from the event are apparently embargoed until Monday, but MVC did say they some of the information may have already been leaked. This all but "confirms" that the game will be Assassin's Creed: Black Flag and will deal with pirates. Above is a supposed map which leaked today, and looks rather legit in it's context. Given the mysterious meeting today, there is no surprise this leaked out.
According to The Examiner, the game will follow Assassin's Creed III and be linked through the Captain Kidd sidequest. All of this, however, remains a rumor until we get some real confirmation on Monday. I am in the middle of my second playthrough of ACIII, and I have to say I am enjoying it more now than I did in my first run. To me, the series hasn't grown stale yet, and I am definitely curious as to how a pirate styled game could function within the given universe.